Perceiving the Past

The Time Lag of Our Senses

Don’t forget: our senses are interpretations of neural events

Sight, sound, touch, taste, smell, even memory — are all nothing but our interpretations of neural events.

Sight, for example, doesn’t reach us instantly as sight. Once light finds the eye, sight then reaches us, eventually (though eventually in this case is counted in milliseconds) as neural signals that we then translate to what we know as and call sight.

The same goes for the other senses. Sometimes, when I meditate on the breath, I think of touch as I feel the air on the nostrils breathing in and then again breathing out, and I realize that what I am feeling is the air on my nostrils as of a few milliseconds ago for the signal, the air-on-sensitive-skin signal takes its sweet time to travel some nerve channels (and possibly via a detour through the spine) before it reaches the brain where yours truly now translates this signal from electro-speak to sense/feeling-speak.

Where I, along with the rest of humanity, learned how to do this (to translate a nerve signal to a specific sense perception) I haven’t a clue, but it’s an interesting question. In fact, I find the whole subject of nerves and signals fascinating.

Courtesy of the University of California at Santa Barbara here is some more detail on neurons and their speeds. They go on to tell us:

“Neurons are some speedy guys. That’s why when we pick up a pencil, it seems as if we immediately know what the pencil feels like. What’s really happening inside our bodies is a little more complex. The instant we pick up that pencil, a group of neurons in our fingers are activated, and fire, super-fast, through our spinal cord all the way up to our brain. How fast, you ask? Try around 75 meters per second fast! If you were driving in a car, that would be more than 150 miles per hour. But it can get even a little more complex than that.

“Neurons transmit an electrochemical signal called the action potential. These signals travel down a part of the neuron called the axon, which is like a wire that carries the signal to other nerve cells. On average a nerve cell sends a signal at about 50 meters per second, which is over 100 miles an hour! This means that when you step on something sharp it does take some time for that signal to go from the nerves in your foot to your brain, although not very much time. In fact, in taller people, it takes longer for a signal to go from one area to another than in shorter people, but the difference is too fast to tell outside of a laboratory.

“Depending on a number of factors, signals can be sent even faster. One important factor is how myelinated the axon is. Myelin is a fatty substance that acts as an electrical insulator, increasing the speed at which the signal is sent. A highly myelinated nerve cell can send a signal at up to 120 meters per second, or nearly 270 miles per hour, quite a bit faster than an airplane taking off! These quick speeds are the basis for everything the nervous system does, from making sense of what your eyes see to deciding what you’re going to have for lunch.

“Neurons transmit their signals from one part of the body to another through long nerve fibers. Depending on the job of the fiber, the speed can change a lot. For instance, some of the nerve fibers that come from your brain and tell your legs to move can travel as fast as 250 miles per hour. For a signal traveling this fast, it takes about 20 milliseconds to travel. However, some signals are much slower like the signals that tell you are being tickled and travel around 1 mile per hour. For this signal, it can take a second or more for you to fully feel it.

“Different nerve fibers send signals faster or slower based on how thick they are, with nerves that send signals faster being thickened. Also, fast nerve fibers also have a protective jacket on them called “myelin” which also makes the signal move faster. Keep in mind that the fastest nerve signals are still about 2.5 million times slower than electricity. So nerve signals have electrical parts to them but are not purely electrical.

“The nervous system is made up of many different types of neurons that all play different roles. You have neurons that transmit commands to your muscles, that respond to touch, pressure, or cold, that respond to pain, and more!

“Each neuron has its own speed it transmits impulses at. Muscle command neurons have one of the fastest speeds (80–120 m/s) which makes sense because during running or other physical activities we often need to make quick adjustments to how we are running and what are body is doing. At that speed, it would take under 9/1000 (.009 or nine thousandths) of a second for a signal to get from your brain to your hand.

“Other neuron speeds vary from .05–2.0 m/s for pain/warmth to 3–30 m/s for touch and pressure. If you have ever grabbed something hot on accident and it has taken a second to realize it, that was caused by the slower neuron speed of pain/warmth neurons.

“The speed of the neuron likely depends on the importance of a quick response. If a muscle command neuron worked at the slower speed of a pain neuron (which happens for some medical conditions), it would be very difficult to walk or keep balance. On the other hand, the slow rate of pain neurons doesn’t result in any major loss of function, so those neurons can be slower.

“Overall, each neuron type has a different speed they operate at in order for the nervous system to function.”

This, as I see it, is the long way of saying that what we perceive via our senses is always, always the past.

And when we talk of the past, there is, of course, also the matter of the external travel a perception has to do before landing on (or in) one of our sense organs.

Light, of course, travels at the speed of, well, light (299,792,458 meters per second to be exact) — but it does travel. Even at that incredible speed, the light travels from the green leaf to then find your eye where the neural signals now generate and set off for your brain and upcoming interpretation (translation).

Sound, as you know, is far, far slower than light (343 meters per second, i.e., 875,000 times slower than light). I remember seeing this very clearly as a kid, watching out farmer-neighbor hammering a metal post into the ground with a sledgehammer. He was about 300 meters away, up there by his barn, and I was fascinated by the delay between seeing the head of the sledgehammer hit the post and the clear and loud metallic sound arriving a second or so later.

Smell doesn’t travel per se; smell particles waft into the air from the flower or milkshake or whatever where they then disburse to eventually find your nose which then neurally signal the brain about the event, where, again, the translation (interpretation) takes place.

Taste and touch don’t have to travel, so the only delay here is the neural travel time.

Buddhism views the mind as a sixth sense, and here the travel time is virtually none, but still, there is some lag involved with calling up (recalling) an image and perceiving it fully.

All such lags aside, what really fascinates me is the amazing translation or interpretation feat we perform with every sense perception. Internally, while different senses travel at different speeds from point of reception to the brain (via the spine), they still appear utterly alike (neural chemical-electrical signals) until we get hold of them and work our magic to convert them to the appropriate sense perception.

How we sort one set of signals from another and then convert them to sight or sound or touch or taste or smell or mental events is nothing short of miraculous. There obviously must exist some sort of conversion table, some sort of lexicon, which we consult (at incredible speed, obviously) to come up with not a neural event but a sight, or a sound on the fly.

Take music. The constant, streaming conversion (translation and interpretation) of signal into music is beyond the beyond — yet we live with it as something so taken for granted that we never stop to think, to amaze, to astound and then just sit back and laugh in wonder.

And even music, the music we hear, is music of the recent past.

© Wolfstuff

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